The present disclosure relates to dental cavity repair and treatment. More specifically, the present disclosure relates to a surface treatment method for targeted dentin and dental materials using a cold atmospheric discharge plasma technique to improve the clinical performance and durability of dental restorations.
Dental fillings are commonly used to treat dental cavities resulting from caries. Caries is the formal name for the disease that causes tooth decay or the formation of what are commonly referred to as cavities. Caries causes tooth decay resulting in decayed matter forming in the tooth, the location of the decayed matter often being referred to as a cavity. As many know, the tooth has an enamel outer layer that covers a thicker layer of dentin. The enamel protects the dentin, and in turn, the dentin protects the pulp of the tooth that contains flesh, including sensitive nerves. Failure of the enamel and the dentin to protect the pulp, whether from accident or caries, is a toothache.
To treat caries, the decayed matter in the cavities needs be removed and the cavities are disinfected and filled. The removal of the decayed matter is usually performed by a dental drill. The materials for the filling are most commonly dental amalgam or composite material. Conventionally, an adhesive is used to firmly connect the tooth to the filling. Adhesives are also used for crowns and caps. A generic term that encompasses fillings, crowns, caps and other structures installed in a tooth to remedy a defect in the tooth is restorations.
Also, one restoration is being replaced with another restoration can be performed. Such replacement is sometimes, but not always, accompanied by the presence of additional decay that needs removal. The prior restoration will usually be removed in the course of this work, sometimes by drilling, but also by other means in situations such as where a crown or a cap is being removed.
The tooth may be formed to have a recess in the tooth, as is common for dental fillings. But the tooth may also be formed into a post or the like, such as when caps are installed.
Where the surfaces of the tooth, adhesive and filling meet each other are called interfaces. For a properly installed filling there is an interface between tooth and adhesive and an interface between adhesive and filling. Fillings have high failure rates at these interfaces and often need to be replaced later.
Failure is particularly prominent in composite dental materials. Composite restoration has become the preferred form of restorative material because of patients' aesthetic requirements and the aversion of patients and dentists to the potential health risk of mercury release from dental amalgams. But composite restorations do not last as long as dental amalgams. Some of the reasons for premature failures of composite restoration include dental composite shrinkage, inadequate bonding of the adhesive to dentin, and formation of a second cavity at the edges of or under the restoration.
Recent studies show that many recorded filling failures occur at the tooth-adhesive interface. These failures are caused by the failure of the adhesive bonding attaching the filling material/composite to the dentin of the tooth. One study has reported that about 70% of composite restoration failures at the back of the mouth occur at the dentin-composite interface. The failure of the adhesive to maintain bonding results in the separation of the composite restoration from dentin. The resulting gaps lead to staining at the margins of the restoration, sensitivity, and recurrent caries, which cause a significant portion of composite restoration removal and replacements.
Studies also show that adhesion between enamel and composite is generally adequate for clinical applications, while adhesive/dentin bonds are the weak link and the interfacial bond strength in the composite restoration deteriorates significantly over time. The disruption of the bonded interface can develop as a consequence of long-term thermal and mechanical stresses, or during the restorative procedure itself, due to stresses generated by composite polymer shrinkage.
Foods and saliva are perpetually in the mouth, and further, bacteria are always present. These can cause problems for the adhesive working to maintain bonding at the restoration-dentin interface. Unsuccessful dentin bonding also means that there are sites at the tooth restoration interface that are vulnerable to hydrolytic breakdown and susceptible to attack by bacterial enzymes. Clinical performance needs to improve when polymer-based dental composites are to be considered viable alternative to dental amalgam. The desired improvements include enhancing the bonding strength at the adhesive/dentin interface to resist polymerization shrinkage and to make it impervious to oral fluids.
Currently, the preparation and disinfection of dental cavities (dentin surfaces) prior to filling relies on mechanical drilling or laser techniques to remove dead (synonymous with necrotic), infected, and non-remineralizable tissue. Both methods are often destructive and can be painful for patients due to mechanical stimulation (vibration) and heating of the dental nerve. To ensure sufficient disinfection, an excess healthy tissue must be removed using the current methods, since dentine contains many small channels in which bacteria can hide. Moreover, the disinfection process itself, with the current methods, can also lead to fracture of dentin.
Several studies and techniques for the preparation/disinfection process have been attempted to improve the interface bonding strength, but with only limited success. For example, U.S. Pat. No. 6,172,130 describes surface treatment of dental prosthesis composed of polymers containing hydrogen atoms using gas phase plasma in a vacuumed reactor vessel operated at 13.56 MHz. The plasma treated polymers are characterized by the hydrogen atoms on the surface of the polymer being partially replaced by fluorine atoms. The type of modified polymers is claimed to be able to improve the retention of the prosthesis and/or limit the development of dental plaque. However, this plasma process, due to its requirement of reduced-pressure environment, is not suitable for surface treatment of the dentin of living subjects in dental clinics.
Therefore, there is a need to develop a new and improved preparation/disinfection method employing the cold atmospheric plasma technology, which can chemically activate dentin surface to implement chemical bonding and enhance adhesion strength at dentin-composite interfaces, and consequently to increase the longevity of dental restorations, as well as to be more cost-effective and less painful to patients.